The plasma membranes of neoplastic cells appear to differ significantly from those of normal cells. The central theme of this project is the continued development and application of spin labeling techniques together with appropriate biochemical measurements in studies membrane model systems and biological membranes, with the aim of understading membranes of normal and malignant tissues. The spin labeling technique consists of introducing a stable nitroxide free radical into the system of interest and observing the behavior of the spin label by electron spin resonance spectroscopy. In previous work we introduced new classes of lipid spin labels (oxazolidine nitroxides rigidly coupled to biologically significant lipids), determined their orientation in stacked phospholipid bilayers, performed a thorough study of motion along fatty acid chains, examined polarity effects and water penetration in lipid bilayers, studied proximity effects, and first described a new lipid phase (boundary lipid) at the lipid-protein interface in the membrane bilayer continuum. The main objectives during the coming year are to extend these observations and methods of analysis to other systems, including sarcoplasmic reticulum ATP'ase and the ATP synthetase complex of the inner mitochondrial membrane, and to begin feasibility studies with cultured cell lines.